This invention relates generally to phase modulation of a laser beam signal carrier conducted through an optical fiber cable, and is related to the disclosure in my prior copending application, U.S. Ser. No. 715,786, filed Mar. 25, 1985, now replaced by continuation application, Ser. No. 436,935 filed Nov. 13, 1989 and the disclosures in U.S. Ser. No. 613,835, filed May 24, 1984, (now U.S. Pat. No. 4,763,030 to Clark et al. issued Aug. 9, 1988) and its parent application, U.S. Ser. No. 438,211, filed Nov. 1, 1982, (abandoned), the present application being a continuation-in-part of all of the foregoing applications because of portions of the disclosures therein in common representing my innovative contributions.
It is generally well known that optical fibers are capable of transmitting information of significantly higher density than electrical conductors because of the high frequency monochromatic beam of coherent light (laser beam) conducted therethrough as the signal carrier. Such high information density transmission has heretofore been limited, as a practical matter, by a relatively narrow bandwidth of the encoding device operatively connected to the laser beam modulator.
Modulation of a laser beam conducted through an optical fiber cable was explicitly proposed for encoded signal generating purposes in my prior copending application, Ser. No. 715,786, aforementioned, while such purpose was inferentially referred to in U.S. Pat. No. 4,763,030 to Clark et al., aforementioned as well as in U.S. Pat. No. 4,433,291 to Yariv et al. According to the invention as claimed in my aforementioned prior copending application, Ser. No. 715,786, stimulated excitation energy is reflected within a resonance cavity formed between spaced end mirrors within an optical fiber core in order to effect analog frequency modulation of the laser beam carrier by magnetostrictive change in cavity dimension. Modulation encoding data was therefore applied magnetostrictively to the resonance cavity portion of the fiber cable through a conductive coating underlying the outer magnetostrictive sheathing.
According to the aforementioned patents to Clark et al. and Yariv et al., phase modulation of a laser beam carrier may be magnetostrictively effected by dimensional change in optical path length caused by strain along a core portion of the fiber cable merely covered by the outer magnetostrictive sheathing. The Clark et al. patent furthermore claims a particular metallic glass composition for the magnetostrictive sheathing that is rendered strain-free by magnetic annealing in order to enhance detection of the magnetic field being sensed as the paramount function of its magnetostrictive activity.
It is therefore an important object of the present invention to provide a system for more directly and economically modulating a laser beam signal carrier conducted through an optical fiber cable for high density data transmission of signals originating from an encoder having a relatively large bandwidth.
A further object in accordance with the foregoing object is to magnetostrictively modulate a laser beam conducted through an optical fiber cable by encoded control and application of a modulating magnetic field having certain beneficial relationships to the outer magnetostrictive sheathing that is annealed to enhance signal carrier modulation.